The present invention relates to new improved compositions and methods for dispersing hydrophilic water-soluble polymers in aqueous liquids.
It is well known in the art that high molecular weight hydrophilic water-soluble polymers (HWSP) are very difficult to disperse or dissolve in aqueous liquids. In dissolving HWSP, conventionally, dry powdered polymer is fed slowly and carefully into the vortex of a vigorously stirred body of water. However, it is frequently difficult to do this in actual operation for a number of reasons. The desired end result is to completely separate and wet each individual polymer particle so no agglomerated particles form, commonly called fish eyes. Mechanical feeders frequently fail and are less than 100% efficient. Sifting polymers by hand is a highly tedious procedure. Often, for example, personnel tend to simply dump the powder into the water, start up the stirrer and expect the material to dissolve. Under such circumstances the polymers swell and ball up into extremely viscous masses with dry and unswollen material inside which the water cannot even reach to dissolve. Many undissolved, so-called "fish eyes," result. Fish eyes may not necessarily float. Fish eyes may also be found sinking to the bottom of the tank, depending on the density of the fish eyes and the aqueous liquid. Under normal circumstances, depending on the particular HWSP, it is impossible to get such a mass to completely dissolve even after hours or even days of stirring. For this reason, a considerable abount of work has been done attempting to develop improved and useful methods for producing dispersions and solutions of HWSP in water. Sometimes the dry powdered polymer is wetted with a water soluble organic solvent or it may be wetted with a surface active material in an attempt to improve the penetration of liquid into the particles, at the same time acting to separate them. (See, for instance, Whelan, U.S. Pat. No. 3,503,895). Considerable fractions of water soluble inert salts, such as sodium chloride or effervescing salts, may be used in order to separate the particles of polymer and reduce their tendency to ball up into insoluble masses. Mechanical feed devices and eductors operated by flowing water have been described and are commercially used for this purpose. Sometimes such devices work well with cold water, but may give considerable difficulty when used with hot water.
Other attempts to disperse HWSP include water-in-oil emulsion techniques with the polymer disposed in the water phase. This system requires an emulsion and is limited in that relatively low concentrations of water soluble polymers have been prepared in the emulsion. Further, the emulsions of this type often tend to be unstable with time.
Certain HWSP such as the various cellulose ethers, xanthan gum, guar gum and the like have been surface treated with crosslinking agents, such as glyoxal, to decrease the rate of hydration of these HWSP in aqueous liquids. In this manner, the HWSP are able to be dispersed before the polymers start to hydrate (solubilize).
Concentrated suspensions of HWSP in inert organic liquids which do not appreciably swell the HWSP have recently been introduced to the drilling industry. Such suspensions generally contain: a high concentration of HWSP; an organic suspending medium such as a hydrocarbon, a relatively high boiling alcohol, and the like; a suspending agent such as an organophilic clay; and a surfactant for enhancing the release of the HWSP into an aqueous liquid. Liquid hydroxyethyl cellulose (HEC) suspensions containing a pH stabilizer are available from NL Baroid/NL Industries, Inc. (LIQUI-VIS) and American Brine and Rental Equipment, Inc. (AMTROL). A formula and method for preparing a liquid HEC suspension published by Union Carbide Corp. consists of 1.39% BENTONE 34 organophilic clay, 0.28% methanol, 42.5% HEC-25, and 2% TERGITOL NP-10 in a hydrocarbon (diesel fuel). Their literature states that patent applications have been applied for on this technology. A formula and method for preparing a liquid HEC suspension published by Hercules Incorporated consists of 37.0% NATROSOL 250-HHW (HEC), 40.1% of an ethyl hexanol premix containing 1% KLUCEL H hydroxypropyl cellulose, 21.1 % ISOPAR M oil, and 1.8% BRIJ SP35 surfactant. A formula and method for preparing a liquid xanthan gum suspension published by Kelco Div., Merck & Co., Inc. consists of 53% mineral oil, 1% EMEREST 2648 surfactant, 1% TRITON x-45 surfactant, 40% KOD85 xanthan gum biopolymer, 1% isopropyl alcohol, and 4% organophilic clay. Diesel fuel can be substituted for the mineral oil provided 7% organophilic clay is used in the liquid polymer composition.
These methods of suspending HWSP suffer from various deficiencies including: incomplete suspension of the HWSP resulting in excessive syneresis and hard packing of the HWSP on storage; an increase in viscosity (hardening) of the suspension on storage, particularly at the elevated temperatures encountered in warehouses during the summer months; and poor dispersion of the HWSP into aqueous liquids under conditions of low shear mixing.
Thus there is a need for improved suspensions of hydrophilic water-soluble polymers which overcome these problems associated with the suspensions currently available.